This invention relates to misfire detection in internal combustion engines, and more particularly, the invention relates to a method and apparatus for sensing misfires in an engine.
There is a need to monitor the combustion in an internal combustion engine, for the purpose of controlling hydrocarbon output. Complete combustion is desirable for maximum output from each piston. Furthermore, complete combustion ensures that all of the fuel is consumed during the combustion process. During a misfire, unburned fuel may be expelled from the exhaust valve, which will enter the exhaust system and increase hydrocarbon emissions. Misfires also contributed to a rough running engine that is noticeable to the vehicle operator.
Presently, one such method uses a pressure sensor to detect the exhaust gas pulse in the exhaust manifold resulting from the opening of the exhaust valves. However, the pressure sensor is only sensitive enough to pick up the opening and closing of the exhaust valve and no information regarding combustion. Pressure sensors typically only detect pressure pulsations of up to approximately 10 Hz. The pressure pulses attributable to a misfire may be in the audible noise frequency range, which may be in the range of 100 Hz–1,000 Hz or more. The prior art pressure sensors are not suitable for detecting misfires.
Misfires are also detected the utilizing knock sensors. Knock sensors utilize an accelerometer that is attached to the exterior of the engine, such as the engine block, to detect the vibration of engine block. The detected vibrations are examined to determine whether they are attributable to a misfire. Knock sensors only determine whether there is a misfire in the engine and are not capable of determining to which piston the misfire is attributable.